Jet pump slip joint with axial grooves

Abstract

A uniform leakage flow device for the slip point of piping systems, and particularly in reactor pressure vessels, selectively imposes a steady, uniform flow of fluid through the slip joint between two adjacent pipe surfaces to thereby eliminate the detrimental flow-induced vibration associated with the unsteady and non-uniform leakage of fluid through the slip joint field. The uniform leakage flow device comprises a plurality of axial grooves that are formed in the wall surface of the slip joint.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, which illustrate what currently is considered to be the best mode for carrying out the invention:

FIG. 1 is a partial, schematic view of a nuclear reactor, shown in cutaway, illustrating a conventional jet pump assembly positioned in the annulus of the reactor;

FIG. 2 is an enlarged view in cross section of a slip joint between the inlet mixer and diffuser of a jet pump;

FIG. 3 is an enlarged view in cross section of a slip joint in which the uniform leakage flow rate device of the present invention is provided;

FIG. 4 is a cross section view taken at line 3-3 of FIG. 3 illustrating the size, number and positioning of axial grooves in the inlet mixer outer wall;

FIG. 5 is an enlarged view in cross section of an alternative embodiment of the invention where the axial grooves are formed in the inner wall of the diffuser; and

FIG. 6 is a cross section view taken at line 5-5 of FIG. 5 illustrating the size, number and position of axial grooves in the diffuser wall.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic illustration of a portion of a conventional reactor pressure vessel (RPV) 20 for a boiling water reactor. Such reactors are previously described in U.S. Pat. No. 4,675,149 and U.S. Pat. No. 6,587,535, the disclosures of which are incorporated herein. The RPV 20 has a generally cylindrical shape and is closed at one end by a bottom head (not shown) and at its other end by removable top head (not shown). A top guide (not shown) is spaced above a core plate 22 within RPV 20. A shroud 24 surrounds the core plate 22 and is supported by a shroud support structure 26. An annulus 28 is formed between the shroud 24 and sidewall 30 of the RPV 20.

An inlet nozzle 32 extends through the sidewall 30 of the RPV 20 and is coupled to a jet pump assembly 34. The jet pump assembly 34 includes a riser pipe 38 and a plurality of inlet mixers 42 connected to the riser pipe 38 by a transition assembly 44. A diffuser 46 is connected to and positioned below each of the inlet mixers. A slip joint 48 couples each inlet mixer 42 to a corresponding diffuser 46.

FIG. 2 is illustrates in an enlarged cross sectional view the relative positioning of an inlet mixer 42 and diffuser 46. It can be seen that the inlet mixer 42 is generally cylindrical and has an outer wall surface 50. The inlet mixer 42 has an open end 58 which is received in an open end 60 of the generally cylindrical diffuser 46. The diffuser 46 has an inner wall surface 52 positioned adjacent to the outer wall surface 50 of the inlet mixer 42. An operational clearance 54 exists at an interface 56 between the outer wall surface 50 of the inlet mixer 42 and the inner wall surface 52 of the diffuser 46. When fluid is pumped through the inlet mixer 42 into the diffuser 46, in the direction of arrow 62, leakage of some of the fluid occurs through the clearance 54 in the slip joint 48, as shown by arrow 64.

Leakage flow from within the jet pump at the slip joint 48 interface between the inlet mixer 42 and the diffuser 46 can become unsteady and non-uniform due to relative lateral motion between the two mating parts, the inlet mixer 42 and diffuser 46. This unsteady slip joint leakage flow is the source of a detrimental vibration excitation in the jet pump assembly 34. High levels of flow induced vibration (FIV) are possible in some jet pump designs at some abnormal operational conditions having increased unsteady slip joint leakage flow rates. Changing the leakage flow characteristics from unsteady flow to steady axial flow through the slip joint can prevent oscillatory slip joint motion and eliminate detrimental, high level FIV.

Thus, FIG. 3 illustrates a first embodiment of the invention where axial grooves 60 are formed in the slip joint 48 interface between the outer wall surface 50 of the inlet mixer 42 and the inner wall surface 52 of the diffuser 48. In this particular embodiment, the axial grooves 60 are formed in the outer wall surface 50 of the inlet mixer 42. As seen more clearly in FIG. 4, a plurality of axial grooves 60 may be formed about the circumference of the inlet mixer 42. In an alternative embodiment shown in FIGS. 5 and 6, the axial grooves 60 may be formed in the inner wall surface 52 of the diffuser.

The number of axial grooves that may be formed in the wall surface (of either the inner mixer or diffuser) may vary, but should number at least four. In a particularly suitable embodiment of the invention, the number of axial grooves formed in the wall surface may be twelve. The number of axial grooves may exceed twelve in number, however.

In a particularly suitable embodiment, the depth (d) of the axial grooves is from two to four times the distance (g) of the radial rap or operational clearance 54 defined between the outer wall surface 50 of the inlet mixer and the inner wall surface 52 of the diffuser 46. The width (w) of the axial groove 60 depends on the additional slip joint leakage flow area introduced by the axial grooves 60. The additional slip joint leakage area, defined as the sum of the areas (w×d) of each axial groove, should be approximately equal to the original slip joint leakage area, or operational clearance 54. The width of the axial grooves can be calculated with the above information and the known outside diameter (D) of the inlet mixer 42.

The number, width and depth of the axial grooves required to produce a uniform and steady leakage flow through the slip joint can be calculated with the following equations, where A is the slip joint leakage area, N is the number of axial grooves, D is the outer diameter of the inlet mixer, w is the width of the axial groove, d is the depth of the axial groove and g is the distance of the radial gap. In the equations illustrated below, the number “3” indicates an exemplar equation where the depth of the groove is three times the measurement (g) of the radial gap.

A=3.14159×D×g=N×w'd=N×w×3×g   Equation 1:

w=3.14159×D×g/(N×3×g)=1.0472×D/N   Equation 2:

The uniform leakage flow device of the present invention may be formed in the slip joint either when the jet pump assembly is new (i.e., non-irradiated) and being positioned in the RPV, or the invention can be formed as a retrofit to an existing RPV. In the first method of formation, the axial grooves are machined into the wall surface of the slip joint, (either in the inlet mixer or the diffuser) prior to coupling of the inlet mixer to the diffuser in assembly of the jet pump.

In the later method of installing the uniform leakage flow device of the invention after the RPV has been in operation, the inlet mixer is removed from the diffuser by means known in the industry. However, because the jet pump has been irradiated during operation of the RPV, the components, comprising the inlet mixer and or diffuser, must be shielded within a water source to protect the workers who are handling the jet pump components. The axial grooves are machined in the wall surface of the inlet mixer or diffuser at the slip joint using tools that may be used underwater. When the axial grooves have been machined into the wall surface of the slip joint, the inlet mixer is re-coupled with the diffuser as is known in the art.

The uniform leakage flow device described herein produces a selected steady and uniform flow of fluid leakage through the slip joint to control detrimental vibration and oscillation in the jet pump assembly. The present invention also enables axial movement of the jet pump components due to varying thermal expansion rates in the components, while maintaining a comprehensive seal at the slip joint. The number and positioning of the axial grooves may vary depending on the particular installation specifications and can be adapted to any variety of piping systems. Therefore, reference herein to particular embodiments and structures of the invention is by way of example only and not by way of limitation.

Claims

1. A uniform leakage flow device for a jet pump assembly having an inlet mixer coupled to a diffuser and defining a slip joint therebetween, comprising: a plurality of axial grooves formed in the wall surface of the slip joint defined between an outer wall surface of the inlet mixer and an inner wall surface of the diffuser.

2. The uniform leakage flow device of claim 1 wherein said plurality of axial grooves is formed in the outer wall surface of the inlet mixer.

3. The uniform leakage flow device of claim 1 wherein said plurality of axial grooves is formed in the inner wall surface of the diffuser.

4. The uniform leakage flow device of claim 1 wherein the number, width and depth of each said plurality of axial grooves is defined by the following equations when the axial grooves area is equal to the slip join leakage area, where A is the slip joint leakage area, N is the number of axial grooves, D is the outer diameter of the inlet mixer, w is the width of the axial groove, d is the depth of the axial groove and g is the distance of the radial gap, then: A=3.14159×D×g=N ×w×d hence,w=3.14159×D×g/(N×d).

5. The uniform leakage flow device of claim 1 wherein the number of axial grooves formed in said wall surface is at least four.

6. The uniform leakage flow device of claim 1 wherein said depth of each said axial groove of said plurality of axial grooves is two to four times the distance of the radial gap of the slip joint, said radial gap being defined as the distance between the outer wall surface of the inlet mixer and the inner wall surface of the diffuser.

7. A method of forming a uniform leakage flow device in the slip joint of a jet pump assembly having an inlet mixer positionable within a diffuser, comprising: forming a plurality of axial grooves in the wall surface of one of the outer wall surface of the inlet mixer or the inner wall surface of the diffuser; and positioning the inlet mixer within the diffuser.

8. The method of claim 7 wherein said axial grooves are formed in said outer wall of said inlet mixer.

9. The method of claim 7 wherein said axial grooves are formed in said inner wall surface of said diffuser.

10. The method of claim 7 wherein said axial grooves are machined in said wall surface underwater.